RE-ENGINEERING THE OCEAN

 In Articles

Naval Architect Jie Zhang looks at the development of offshore mooring systems in challenging environments

Mooring in challenging environments, both very deep and very shallow waters, presents multiple issues for the anchoring of floating offshore wind platforms.

These range from selecting the most cost-efficient mooring system, to mitigating the strong dynamic motions of waves in shallower waters.

Mooring systems are a crucial component of a floating offshore wind installation. However, there is a level of uncertainty surrounding floating specific mooring systems in terms of project risk and lifetime cost.

While most offshore wind turbines are anchored to the ocean floor on fixed foundations, limiting them to depths of about 165 feet, floating turbines are tethered to the seabed by mooring lines. These enormous structures are assembled on land and pulled out to sea by boats.

One of our specialisms at Solis Marine Engineering is understanding the different mooring technologies and evaluating these based upon specific scenarios such as floater design, water depth, ocean and marine growth conditions.

We also need to factor in the likelihood and impact of mooring failure specific to floating offshore wind systems.

This means undertaking expert analysis to understand the root cause failures within traditional oil and gas installations and how these could potentially translate to failure rates in floating offshore wind projects.

Each project is a complex challenge and collaboration between all partners is key.

There are currently three main mooring designs:

  • The spar-buoy has a long, weighted cylinder tube which extends down from the turbine and below the ocean’s surface to balance it.
  • Semi-submersible platforms which are modular and made up of floating cylindrical structures secured by mooring lines.
  • The tension-leg structure has a smaller platform anchored to the seabed with taut mooring lines for deeper water.

However, as the floating offshore wind sector continues to grow in Asia Pacific and Europe, a range of concepts and designs are being investigated to advance the range of anchoring devices and mooring configurations.

Some involve multiple floaters that are moored together, or multiple mooring lines with shared anchors.

Different components are also being researched, developed and tested. Low stiffness synthetic lines are being augmented and constructed in ways that make them more fatigue-resistant to accommodate long design lives.

And more traditional mooring components are being combined in varying ways to achieve composite stiffnesses that achieve preferred station-keeping performance characteristics.

Mechanical devices that offer a more compact way of providing design specific stiffness characteristics and load monitoring capability are also being developed.

Going forward, streamlining the number of concepts under developed will be key to cost reduction.

Anchors away

The ability to install turbines in deeper waters, where winds tend to be stronger, opens up huge amounts of the ocean to generate renewable wind power.

However, floating offshore wind is still in its early stages: only about 80 megawatts of a total of about 32 gigawatts (0.25%) of installed offshore wind capacity is floating.

But some experts say the relatively new technology could become an important part of the renewables energy mix if the sector can overcome the hurdles of cost and design.

This is where we come in. Solis Marine Engineering brings to the offshore renewables sector extensive experience in hydrostatic and hydrodynamic analysis, mooring analysis, subsea cable analysis, installation analysis, project management and planning.

Solis Marine Engineering is currently recruiting for a Structural Engineer to join our Singapore office. Applications and CVs should be sent to solis@solis-marine.com

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